I run an odd size tire. Dug around some and found a 'rule of thumb', which is temperature based. Increase your 'cold' pressure until your 'hot' pressure is 10% more. That is the minimum cold pressure you can run. Since the TPMS reports relative pressures pretty repeatably, it only takes a few days of experimentation to find the floor. After that season with pressure until you like the ride.
For me 35 psi is the floor based on load rating. 36 or 37 is the floor based on tire psi change, and 37 is where it rides best.
All provisios and at your own risks apply.
Exactly this and the chalk test are the best methods for dialing in pressure.
P285/70/17 AT3 117T here and have been playing with this for some time.
Its important to note that "cold" pressure should be measured at ambient temperature.
When inflating in my garage, its often 20 degrees cooler than ambient. The pavement/highway will also be significantly hotter than that.
Rule of thumb here is 1PSI gain/loss for every 10 degrees F.
For my ideal 34-36 "cold", im inflating to 32-33 in my garage. The pressure is stabilizing at around 36 PSI which is my target.
Anything above 38 at temp is starting degrading my ride quality.
You want no more than a 10%-20% gain from the heat/friction at "hot" but it also does not help that ambient is varying by 20-30 degrees F daily in Texas...
Ive continued to do more testing of my setup and im beginning to realize ive probably made a mistake going to P rated.
In order to achieve the best ride, I'm sacrificing a lot of stability.
Testing at a cold 30 PSI made me lose a lot steering control to the point I was feeling the wheel wobble on turns.
Scary to say the least given it was no more than 15-20mph and it felt as if the sidewall was giving in on my inside wheel.
Im starting to think that this vehicle is just too heavy for my tire choice, and im running "light" with no third row and no occupants.
Someone had mentioned this before in a comment and I think I agree.
At least this is my observation running such a high sidewall.
If i were running a leaner profile ratio, I doubt these effects would persist due to the reduction in moment arm of the forces applied.
And all of this is happening well above the recommended inflation for this spec.
It would make sense that a stiffer tire in a E load, inflated to around half its maximum pressure would give me an equivalently compliant ride but with added rigidity. I would love to be able to do some comparison driving with anyone in my area.
I also recognize that with no occupants and less weight than "stock" there are some effects from being over-sprung. This was the same in my 470.
The more loaded the springs are, the more AHC can have an impact with adjusted damping.
Any help / experience / advice is appreciated, so let me know your thoughts.
Thanks!
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